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Public advisoryEdit

TROPICAL STORM CHAN-HOM PUBLIC ADVISORY NUMBER 17

WIKI-HURRICANES FORECASTING CENTER

12:00 PM JST SAT JUL 04 2015

...CHAN-HOM IMPROVING IN ORGANIZATION...

SUMMARY OF 12:00 PM JST...03:00 UTC...INFORMATION

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LOCATION...12.9N 147.3E

CENTER POSITION CONFIDENCE: HIGH

ABOUT 175 MI...280 KM SE OF HAGATNA, GUAM

MAXIMUM SUSTAINED WINDS...45 KT...50 MPH...85 KM/H

MINIMUM BAROMETRIC PRESSURE...999 MB...29.50 INCHES

PRESENT MOVEMENT...N AT 8 KT...9 MPH...14 KM/H

DISCUSSION AND 48-HOUR OUTLOOK

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At 12:00 pm JST, the center of Tropical Storm Chan-Hom was situated near 12.9N, 147.3E, or about 175 miles (280 km) southeast of Hagatna, Guam. Maximum sustained winds were 45 knots (50 mph, 80 km/h), with higher gusts. The minimum barometric pressure was 999 millibars (hPa; 29.50 inHg), and the cyclone was tracking northward at 8 knots (9 mph, 14 km/h). Environmental conditions are becoming increasingly favorable, and steady to rapid intensification is expected throughout the forecast period.

NEXT ADVISORY

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Next complete advisory at 6:00 pm JST.

$$

Forecaster TAWX14

DiscussionEdit

TROPICAL STORM CHAN-HOM PUBLIC DISCUSSION NUMBER 17

WIKI-HURRICANES FORECASTING CENTER

12:00 PM JST SAT JUL 04 2015

Although still quite irregular, Chan-hom has organized a bit this evening. Deep convection has been expanding in aerial coverage and intensity, and the low-level circulation is now safely obscured from view. Banding features are becoming more prominent throughout the eastern semicircle, and upper-level outflow is expanding to the south. A 2332z ASCAT MetOp-B pass indicated that the actual center was very elongated in nature, and the overall configuration more resembles an open trough rather than a tropical cyclone. Nonetheless, the pass showed several areas of 35kt winds. Given the low bias of the instrument and the fact that it did not sample the entire cyclone, the initial intensity has been held at a possibly generous 45kt.

The formation of deep convection and expanding upper-level outflow suggests that atmospheric dynamics are becoming more favorable for intensification. In fact, maps from UW-CIMSS indicate that vertical wind shear has fallen 10-20 knots in the vicinity of Chan-hom since this time yesterday. With sea surface temperatures on the order of 29-30C, plenty of ocean heat content, and sufficient mid-level moisture, steady strengthening is forecast over the next few days. Once an inner core is established, the potential for rapid intensification is high. The GFS and HWRF continue to indicate that Chan-hom will exceed the Category 5 threshold by the end of the forecast period, whereas the ECMWF only shows the system as a Category 3-equivalent at the same time. Given the forecast parameters, more weight is being placed on the GFS/HWRF, and the updated intensity forecast is not much different from the previous advisory package.

A mid-level trough has acted over the past 24 hours to weaken the 594dm mid-level ridge to the north of Chan-hom, allowing the cyclone to move northward and at times northeastward. However, over the subsequent day, this ridge is expected to re-intensify and force Chan-hom on a northwestward motion. After 72 hours, as the system approaches the western extent of the anticyclone, the storm should turn increasingly poleward. The updated WHFC forecast is slightly farther north in the short term to account for the erratic center motion over the past day, but it is generally unchanged several days out.

INIT 04/0300Z 12.9N 147.3E 45 KT 50 MPH

12H 04/1200Z 13.9N 146.6E 50 KT 60 MPH

24H 05/0000Z 15.3N 145.7E 55 KT 65 MPH

36H 05/1200Z 16.2N 144.6E 65 KT 75 MPH

48H 06/0000Z 17.5N 142.7E 80 KT 90 MPH

72H 07/0000Z 20.4N 138.4E 105 KT 120 MPH

96H 08/0000Z 24.0N 133.8E 120 KT 140 MPH

120H 09/0000Z 27.7N 129.3E 130 KT 150 MPH

$$

Forecaster TAWX14

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